However when viewed from a more side on perspective they are somewhat less mysterious. They are outgassing events, or geysers blasting dark material out onto the suface in a radial pattern. Not plants or bacterial mats. This picture gives a good view:

In a snese though this is just as impressive. The exact nature of the dark material is unknown and the very process itself shows that there is enough subsurface heat to form complex geological processes. That heat could be used in other ways and by other processes hint, hint.